This application claims priority to an application entitled xe2x80x9cMobile Communication System Having Multi-band Antennaxe2x80x9d filed in the Korean Industrial Property Office on Oct. 13, 2001 and assigned Serial No. 2001-63239, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly to a mobile communication system having a multi-band antenna, which may be employed in a portable mobile communication system and allows the communication to be smoothly carried out in different frequency bands.
2. Description of the Related Art
Mobile communication systems have made surprising commercial progress not only in Korea but also in the world. All over the world, one important step in the progress of mobile communication systems is the change from analog transmission to digital transmission. On the basis of digital transmission, mobile communication systems having dual operation modes, that is, which can be operated in either CDMA or PCS mode, are now being developed as private portable mobile communication systems.
Further, according to the regulation E911 of the Federal Communication Commission (FCC) it is anticipated that future mobile communications in the United States should provide a global positioning function. E911 of FCC recommends that mobile communication terminals should be able to transmit their location, that is, should be traced by a wireless positioning system, for example, by a global positioning system (GPS) satellite. Therefore, mobile communication terminals will be required to have an antenna capable of receiving the signal of GPS band, which is 1.575 GHz.
In general, a mobile communication terminal capable of receiving the GPS signal employs a chip-type GPS antenna, which will be described in detail hereinafter.
FIG. 1 is a schematic view including a block diagram of a conventional mobile communication system capable of receiving signals of triple bands. FIG. 1 shows the construction of a mobile communication terminal 10 for performing communication by receiving either a signal of the GPS band or other signals of other bands. The mobile communication terminal 10 has two antennas which selectively receive signals of bands different from each other.
That is, in the mobile communication terminal 10, signals with frequencies of CDMA and PCS bands are synchronized and received by a dual band antenna 12, while a signal with a frequency of the GPS band is synchronized and received by a GPS antenna 30. xe2x80x9cDual Band Antenna for Wireless Transmitter/receiverxe2x80x9d disclosed in Korean Patent Laid-Open No. 1999-0072602 and U.S. Pat. No. 6,198,440 B1 issued to Samsung Electronics, Co., Ltd., the contents of which are incorporated by reference, describes an antenna that may be utilized as the dual band antenna 12, while a GPS band antenna realized as a chip may be utilized as the GPS antenna 30.
A signal with a frequency of the CDMA/PCS bands received by the dual band antenna 12 is supplied to a separator 50 through a matching circuit 40, which matches impedance between the dual band antenna 12, and a circuit in the mobile communication system. The separator 50 separates the signal with frequencies of CDMA/PCS bands received through the dual band antenna 12 into a signal with a frequency of CDMA band and a signal with a frequency of PCS band, and supplies the separated signals to a CDMA duplexer 60 and a PCS duplexer 70, which are connected with output terminals. In addition, the separator 50 supplies a signal received from the CDMA duplexer 60 or the PCS duplexer 70 to the dual band antenna 12 through the matching circuit 40.
FIGS. 2 and 3 are Smith charts that illustrate impedance matching characteristics of the dual band antenna 12 at the CDMA/PCS bands when it is in retracted and extended states in free space, obtained from measurements by means of a mobile communication phone model SCH-8500, which is produced and sold by Samsung Electronics, Co., Ltd., in which the dual band antenna 12 having the same construction as that in the disclosed in U.S. Pat. No. 6,198,440 is employed. In this case, the impedance was measured at connection nodes between the separator 50 and the CDMA/PCS duplexers 60 and 70. The impedance matching characteristics is measured by using a Network Analyzer 8753E manufactured by Agilent company. A vertical axis in graph of FIGS. 2 and 3 indicates Voltage Standing Wave Ratio (VSWR) where a bottom value is 1 and its value is increased upward by one per each division in the graph. And, a horizontal axis in graph of FIGS. 2 and 3 indicates Frequency. Also, in graph of the FIGS., frequency and VSWR as to the points 1 to 5 indicated as xcex94 are mentioned on right side and top part, respectively. For example, in FIG. 2, the frequency of xcex94 1 is 824 MHz and the VSWR of xcex94 1 is 1.5399. The above are applicable identically to the other figures showing impedance matching characteristics in this application. Further, FIGS. 5 to 8 illustrate antenna gain patterns at the CDMA/PCS bands in free space, obtained from measurements for the dual band antenna 12 employed in the above mobile phone model.
The two duplexers 60 and 70 each supply the CDMA and PCS band frequencies separately outputted from the separator 50 to CDMA RF section 110 comprising communication signal processing section and PCS RF section 120, and also supplies the RF signal outputted from the CDMA RF section 10 and PCS RF section 120 to the separator 50. The CDMA RF section 110 modulates the signal received from the CDMA duplexer 60 and supplies the modulated signal to the controller 90, or modulates a signal to be transmitted that is inputted from the controller 90 and supplies the modulated signal to separator 50. The PCS RF section 120 modulates the signal received from the PCS duplexer 70 and supplies it to the controller 90, or modulates the signal to be transmitted that is inputted from the controller 90 to a signal of a PCS band and supplies it to the separator 50.
The controller 90 has the functions of a control section in a general dual mode mobile communication system such as a mobile phone usable as either a CDMA or a PCS mobile phone. Therefore, the controller 90 either reproduces the voice from a signal received from the CDMA RF section 110 or the PCS, or supplies the voice signal to the CDMA RF section 110 or the PCS RF section 120.
Meanwhile, a GPS filter 80 connected with the GPS antenna 30 filters signals received thereto and passes only the GPS band signal, thereby supplying it to a GPS signal processing unit 100 in controller 90. The GPS signal processor 100 demodulates a signal of GPS band inputted thereto, thereby generating three-dimensional information for global positioning.
FIGS. 4 and 9 illustrate impedance matching data at the GPS band in free space state and an antenna gain pattern in a retracted state, obtained from measurements by means of the GPS antenna 30 employed in the above mobile communication phone model SCH-8500.
However, the conventional mobile communication system having the construction as shown in FIG. 1 is disadvantageous in that it has a separate GPS antenna 30 for receiving the signal of GPS band, which makes the construction of the system complicated.
Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a mobile communication system which has an antenna construction capable of smoothly receiving frequencies of three bands which are different from each other.
It is another object of the present invention to provide a mobile communication system which employs an integrated antenna having a dual helical construction capable of receiving frequencies of either the CDMA/PCS bands or the GPS band with a minimum of loss.
It is still another object of the present invention to provide a mobile communication system which may have either a fixed type antenna employing a dual-pitch helical antenna or a retractable type antenna employing a dual-pitch helical antenna along with a whip antenna, and which can effectively receive signals of different frequency bands by means of a switch element capable of effectively operating for multi-band signals and separating triple band signals from each other.
In order to accomplish these objects, there is provided a mobile communication system having a multi-band antenna, comprising: a GPS processing section for receiving a signal of a first frequency band, so as to generate global positioning information; a communication signal processing section for receiving signals of a second frequency band and a third frequency band, demodulating the received signals, and modulating signals to be transmitted of the second frequency band and the third frequency band and outputting the modulated signals, the second frequency band being lower than the first frequency band and the third frequency band being higher than the first frequency band; a multi-band antenna for receiving and transmitting signals of multiple frequency bands including the first to third frequency bands, the multi-band antenna including a dual-pitch helical antenna which includes first and second helical coil portions connected in series, the first and second helical coil portions having pitches different from each other so that the first and second helical coil portions have different impedances for the signals of the first to third frequency bands; a frequency band separator section connected between the multi-band antenna and the GPS processing section and communication signal processing section, the frequency band separator section supplying the signal of the first frequency band to the GPS processing section while supplying the signals of the second and third frequency bands to the communication signal processing section, among the signals of multiple frequency bands received by the multi-band antenna, the frequency band separator section supplying signals, which are outputted from the GPS processing section and the communication signal processing section to the multi-band antenna; and a control section for controlling the GPS processing section and the communication signal processing section.
It is preferred that the multi-band antenna is a retractable type antenna employing a dual-pitch helical antenna along with a whip antenna. Also, it is preferred that the multi-band antenna is a triple-band antenna capable of receiving signals of not only dual bands of CDMA/PCS but also a GPS band.
The frequency band separator section comprises: a switch for forming an electric wave path between the multi-band antenna and the communication signal processing section, the switch changing the electric wave path by connecting an electric wave path of the multi-band antenna to the GPS processing section in response to a path control signal outputted from the control section; a separator disposed between and connected to the switch and the communication signal processing section, the separator separating and outputting signals of the second and third frequency bands, and supplying signals of the second and third frequency bands to the switch; and a CDMA duplexer and a PCS duplexer for supplying the signals of the second and third frequency bands outputted from the separator to CDMA and PCS RF sections in the communication signal processing section, respectively, and for supplying signals of the second and third frequency bands, outputted from the CDMA and PCS RF sections, to the separator, respectively.
The control section sends the path control signal to the switch for a predetermined period of time in response to an E911 mode, and controls the GPS processing section and the communication signal processing section.
In accordance with another aspect of the present invention, the frequency band separator section may comprise: a duplexer for separating signals received from the multi-band antenna into a signal of the second frequency band and signals of a frequency band higher than the second frequency band, the diplexer supplying the signal of the second frequency band to a CDMA RF section in the communication signal processing section; a separator for separating the signals of the frequency band higher than the second frequency band into the signals of the first and third frequency bands, supplying the signal of the first frequency band to the GPS processing section, and supplying inputted signals of the first and third frequency bands to the diplexer; CDMA duplexer for supplying the signal of the second frequency band to CDMA RF section in the communication signal processing section; and a PCS duplexer for supplying the signal of the third frequency band to a PCS RF section in the communication signal processing section.
In the mobile communication system having either construction described above according to the present invention, the number of turns and pitches of each coil portion of the dual-pitch helical coil can be properly selected so as to realize a multi-band antenna capable of having at least two resonance frequency bands. Further, in the mobile communication system, the frequency band separator section separates low frequency band signals such as CDMA/PCS communication signals, GPS signal, or CDMA signal, as well as high frequency band signals such as GPS/PCS signals, from each other, thereby enabling the mobile communication system to perform the E911 mode service in addition to the dual band (CDMA/PCS) communication services. Furthermore, the present invention realizes a more compact mobile communication system capable of receiving signals of various frequency bands different from each other through one antenna.